The application generally relates to grounding systems. The application relates more specifically to grounding systems for semiconductor power components with a nonconductive heatsink.
Variable speed drives (VSDs) used for heating, ventilation, air-conditioning and refrigeration (HVAC&R) applications can use heat sinks or cooling blocks for mounting and thermal management of semiconductor devices, for example, insulated gate bipolar transistor semiconductor switches. The heat sink can be constructed of metal that has a high coefficient of thermal conductivity, for example, copper. However, metal heat sinks can be expensive due to material and labor costs associated with manufacturing the heat sink. VSDs may also use heat sinks constructed of nonmetallic materials, for example, plastic, which reduce material costs. The use of plastic heat sinks, however, may still require costly machining, as plastic heat sinks typically are not suitable for injection molding manufacturing because of their large size and low usage quantities. The size of a particular heat sink is usually determined by the number of semiconductor components which are to be mounted on the heat sink.
One type of semiconductor component that can be mounted on a heat sink is a semiconductor module. A semiconductor module may include a base on which one or more semiconductor devices are mounted. The base of the semiconductor module and an upper conductive layer of the semiconductor module can be separated by a substrate layer disposed between the individual semiconductor devices and the base. Semiconductor devices, or chips, used in semiconductor modules may include insulated-gate bipolar transistors (IGBT), bipolar junction transistors (BJT), metal-oxide semiconductor field-effect transistors (MOSFET), semiconductor controlled rectifier (SCR), and other suitable three terminal semiconductor devices. The substrate may cause there to be parasitic capacitances between semiconductor devices and the base, and between the upper conductive layer and the base.
The use of plastic heat sinks with semiconductor modules may cause parasitic currents and electrical charges to build up between the base of the semiconductor module and the current conductors within the semiconductor module. Such parasitic currents and electrical charges may interfere with control signals for the semiconductor module, thus causing some semiconductor devices within the module to enter an “ON” or conductive state when they would normally be required by the control signals to be in the “OFF” or nonconductive state. The plastic or nonconductive heat sink causes the base of the semiconductor module to be electrically isolated from the rest of the system; hence, any parasitic current induced by the rate of change of voltage applied to the module can circulate within the module, thus potentially interfering with low level control signals and causing the module to malfunction. There is therefore a need for a method and system which enables safe and reliable operation of semiconductor modules mounted onto a nonconductive heat sink.